The present invention relates generally to heating and cooling systems and more particularly to a heating and cooling system constructed to maintain a common fluid flow direction to achieve the desired thermal exchanges associated with operation of a heat pump during both heating and cooling operations.
FIGS. 2 and 3 are graphic representations of an exemplary heating and cooling system, or heat pump, and the components associated therewith. Referring to FIGS. 2 and 3, such systems commonly include a heat exchanger 10, that includes a first fluid loop 12 associated with a fluid whose temperature varies as a function of thermal interaction and a second fluid loop 14 associated with a working fluid. Such systems commonly include a compressor 16, an evaporator 18, a reheater 20, one or more valves 22, and a four-way or reversing valve 24 whose orientation is associated with the direction of fluid flow associated with the conduits to which it is engaged, or as shown in FIGS. 2 and 3, the direction of fluid flow associated with fluid loop 14 relative to hear exchanger 10.
In a common configuration, a refrigerant-air heat exchanger exposed to a process airstream increases or decreases the air temperature during separate modes of operation as associated with the demands associated with the application conditions. Referring to FIG. 2, when cooling or dehumidification of the process airstream is required, heat exchanger 18 is utilized as a refrigerant evaporator. An expansion device 22 located upstream of heat exchanger 18 reduces the pressure of the liquid refrigerant before it returns to heat exchanger 18 such that the refrigerant absorbs energy from the process airstream thereby decreasing the sensible and latent temperature of the airstream.
Referring to FIG. 3, during the alternate operating mode associated with increasing a process fluid temperature or flow heating activities, heat exchanger 18 is utilized as a refrigerant condenser. High temperature refrigerant vapor is introduced into heat exchanger 18 and condensed to liquid refrigerant as it is cooled by the process air. In either operating mode, heat exchanger 18 is exposed to working and refrigerant fluid flows but is operable as a refrigerant condenser or refrigerant evaporator in order to absorb or reject heat associated with fluid flow 14 as the situation or application may require. As shown in FIGS. 2 and 3, many such systems maintain a common direction associated with fluid flow 12 and reverse the direction of flow associated with the refrigerant fluid flow 14, as indicated by the opposite directional arrows associated with fluid flow 14 with respect to FIGS. 2 and 3, to achieve the alternate heating and cooling functions.
Redirection of refrigerant flow 14 is commonly achieved via operation of a valve or plurality of valves, such as reversing valve 24. The orientation of the one or more valves facilitates reversal of the direction of travel associated with fluid flow 14 through heat exchanger 10. Due to the fixed flow paths within heat exchanger 18, pressure differentials and velocities vary significantly as either warm vapor or cooled liquid associated with fluid flow 14 are directed therethough. Heat exchanger 18 must be designed and constructed to maintain desired fluid flow velocities to achieve a desired condition associated with the return of the refrigeration fluid when the system is utilized in the cooling mode. Such considerations increase the fluid pressure at compressor 16 when the system is operated in the heating mode as the pressure differential though heat exchanger 18 increases due to the higher volumetric flow rates at relatively similar mass flow rates.
Such concerns commonly result in the generation or utilization of larger heat exchangers for thermal counter flow configurations wherein the log mean temperature differentials of the heat exchange fluids are highest. Reversing the physical flow of refrigerant lessens the efficiency of the thermal exchange associated with operation of heat exchanger 18 as doing so creates a thermal parallel flow and lower log mean temperature differential. Such considerations commonly result in utilization of a fluid flow heat exchanger or heater that is associated with the working fluid flow and the airflow associated with the airstream associated with utilization of heat exchanger 20. Such a configuration increases the temperature of the process air when the system is operated in the cooling mode and is advantageous where latent cooling of the process air is required and limited or no detectable or sensible cooling is required. The secondary heat exchanger is commonly not utilized during operation of the system during the heating modes such that other components of the system must be configured to accommodate the flow parameters associated with the cooling demands.
Therefore, there is a need for heating and cooling systems that can achieve desired thermal exchanges associated with operation of a heat pump during both heating and cooling operations. There is also a need for a heating and cooling system constructed to maintain a common fluid flow direction when used for both heating and cooling operations